Namespaces are collections of parameters and operations in which their names are unique. The advantage of using namespaces is that the WSDL can define terms, like string, just by referring it its namespace, xs. Also, prepending the namespace to a parameter ensures that there is no danger of name collisions.
Each namespace declaration starts with "xmlns:" (XML namespace:) and is followed by the abbreviation for the namespace. For example, in the following namespace declaration, xs becomes the abbreviation for the URL of the schema.
Throughout the remainder of the WSDL you will see parameters defined in terms of namespace abbreviations, for example:
These abbreviations provide the namespace in which the parameters are defined.